Cam follower assemblies

ABSTRACT

A cam follower assembly comprises two followers biased apart, in a direction transverse to the movement controlled by the cam, against two cam faces. By attaching the element moved to one follower, movement in either direction is controlled by one cam face, and accurate control can be achieved with a small assembly.

United States Patent 1191 Massey CAM FOLLOWER ASSEMBLIES [75] inventor: Richard Anthony Massey, Sheffield,

England 731 Assignee: The Rani: Organisation Limited,

London, England [22] Filed: Dec. 22, 1971 [2!] Appl. No.: 210,934

[52] [1.8. CI. 74/99, 74/569 [51] Int. Cl. Fl6ll 21/44 [58] Field of Search 74/89, 569, 568, 74/567, 99

[56] References Cited UNITED STATES PATENTS 3,344,685 10/1967 Crouzet 74/569 2,477,127 7/l949 Holtz 74/569 Aug. 28, 1973 3,475,972 11/1969 Steibel 74/25 2,425,898 8/1947 Riegei 74/89 FOREIGN PATENTS OR APPLICATIONS 912,203 4/1946 France 74/99 Primary ExaminerCharles J. Myhre Assistant Examiner-Wesiey S. Ratliff, Jr. Attorney-Holcombe, Wetherili & Brisebois [57] ABSTRACT A cam follower assembly comprises two followers biased apart, in a direction transverse to the movement controlled by the cam, against two cam faces. By attaching the element moved to one follower, movement in either direction is controlled by one cam face, and accurate control can be achieved with a small assembly.

5 Claims, 3 Drawing Figures CAM FOLLOWER ASSEMBLIES This invention relates to cam followers. It is particularly useful in cam systems for zoom lenses and a specific embodiment described below illustrates such an application, but the invention is not limited to such a use.

In any cam system, relative displacement in the direc tion between a cam and a cam follower assembly causes relative movement in a second direction.

One object of this invention is to provide a cam follower assembly which allows movement in either sense in the second direction to be controlled by the same cam profile.

Another object is to provide a cam follower assembly whose dimension in the second direction is small.

Accordingly, the present invention provides a cam follower assembly for co-operating with a cam having a control face and a back-up face, the assembly comprising a base member, a control cam follower mounted on the base member for co-operation with the cam control face, and a back-up cam follower connected to the base member by resilient means for biasing into engagement with the cam'back-up face, the control and back-up cam followers being disposed to the direction of movement of the assembly controlled by the control face.

Preferably, the cam followers are disposed so that the line joining their centres is perpendicular to said direction.

Each cam follower may suitably be a roller journalled for rotation along its respective cam face.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:

FIG. 1 illustrates a zoom lens assembly incorporating a cam follower according to this invention;

FIG. 2 is a partial section taken on the line A-A of FIG. 1; and

FIG. 3 shows the cam follower with the developed cam profile superimposed.

Referring now to the drawings, a zoom lens assembly includes a tubular sleeve 10 having cut in it a camslot 12. A cam follower assembly 14 mounted inside the sleeve has a base member 16 to which is attached a lens element (not shown) which is moved axially of the sleeve 10 to adjust the focal length (zoom) or focus of the lens assembly. Thus a cam slot 12 and follower assembly l4 co-operate to allow adjustment of zoom or focus to be made by rotating the sleeve 10. The axial movement of the follower assembly 14 is controlled by a control face 18 of the cam slot 12 and a back-up face 20 of the slot 12 assists in this control and in preventing backlash, as will be explained.

Turning now to the follower assembly 14, a first roller 22 constitutes a control cam follower and is journalled on the base member 16 for rotation along the control face 18. A second roller 24 is journalled on a support 26 for rotation along the back-up face 20. The support 26 is slidingly mounted on the base member 16 and is biased in a direction parallel to the lens axis by a coil spring 28. The rollers 22, 24 are disposed equidistantly on either side of the lens axis with their axes equally spaced from and parallel to a line perpendicular to the lens axis.

Thus, as best seen in FIG. 3, as the sleeve 10 is rotated in the direction 8, the follower assembly 14 (and hence the lens element) move in the direction C in a manner which is controlled entirely by the control face 18. The spring 28 both urges the rollers 22, 24 into contact with the faces 18, 20 thus minimising backlash in the follower assembly, and also takes up any irregularity in the profile of the back up face 20.

The follower assembly according to the invention thus allows movement in the direction C to be controlled by a single cam face, and the back-up face need not be cut with the accuracy required for the control face.

Further, the disposition of the rollers allows the use of a cam slot of small axial dimension, thus reducing the rotating mass, and either a follower assembly of small axial dimensions or the employment of larger diameter rollers for a given size of cam slot with a consequent reduction in wear. Also, since the roller axes are parallel, the distance of the rollers radially from the lens axis is not critical and the cam form will be reproduced accurately provided only that the rollers are maintained in contact with the cam faces.

I claim:

1. A cam follower assembly for co-operating with a cam having a control face and a back-up face, the assembly comprising a base member, a control cam follower mounted on the base member for co-operation with the cam control face, and a back-up cam follower connected to the base member by resilient means for biasing said back-up cam follower into engagement with the cam back-up face, the control and back-up cam followers being disposed so that the line joining their centers is transverse to the direction of movement of the assembly controlled by the control face.

2. An assembly as claimed in claim 1, in which the cam followers are disposed so that the line joining their centres is perpendicular to said direction.

3. An assembly as claimed in claim 1, in which each cam follower is a roller journalled for rotation along its respective cam face.

4. An assembly as claimed in claim 1, in which the resilient means is a coil spring.

5. In an assembly including a first member definingfirst and second cam faces and adapted for movement in one direction, and a second member carrying cam follower means cooperating with said cam faces to cause movement of said second member in a second direction in response to movement of said first member in said first direction, the improvement wherein said cam follower means comprises a base member, a first cam follower mounted on the base member for cooperation with said first cam face, a second cam follower, and resilient means connecting said second cam follower to said base member, said cam followers being disposed with the line joining their centres oblique to said second direction.

' l t t UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3.54. 473 Dated, Au ust 28. 1972 Inventor-(s) RICHARD ANTHONY MASSEY It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

[30] Foreign Application Priority Data January 27, 1971 Great Britain 33 3/71 Signed and sealed this l9th day of March l 974.

(SEAL) Attest:

EDWARD M.FLE TCHER,JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PC4050 (WGQ) uscoMM-oc scan-p59 UTS. GOVERNMENT PRINTING OFFICE I989 0-365-334. 

1. A cam follower assembly for co-operating with a cam having a control face and a back-up face, the assembly comprising a base member, a control cam follower mounted on the base member for cooperation with the cam control face, and a back-up cam follower connected to the base member by resilient means for biasing said back-up cam follower into engagement with the cam back-up face, the control and back-up cam followers being disposed so that the line joining their centers is transverse to the direction of movement of the assembly controlled by the control face.
 2. An assembly as claimed in claim 1, in which the cam followers are disposed so that the line joining their centres is perpendicular to said direction.
 3. An assembly as claimed in claim 1, in which each cam follower is a roller journalled for rotation along its respective cam face.
 4. An assembly as claimed in claim 1, in which the resilient means is a coil spring.
 5. In an assembly including a first member defining first and second cam faces and adapted for movement in one direction, and a second member carrying cam follower means cooperating with said cam faces to cause movement of said second member in a second direction in response to movement of said first member in said first direction, the improvement wherein said cam follower means comprises a base member, a first cam follower mounted on the base member for cooperation with said first cam face, a second cam follower, and resilient means connecting said second cam follower to said base member, said cam followers being disposed with the line joining their centres oblique to said second direction. 